Many large scale manufacturing facilities generate extremely large quantities of waste energy, typically in the form of heat, during the performance of their manufacturing operations. This waste energy is completely lost after use and, in fact, is conventionally vented directly to the atmosphere. Attempts at energy recovery through available techniques are either highly inefficient or so costly as to prohibitively exceed the savings which might result therefrom due to the energy recovered.
One of the best examples of the above situation exists in the pulp and paper industry in which huge equipment installations, which necessitate the use of extremely large amounts of energy, are required to produce tons of pulp and paper on a daily basis. Equipment of this nature must also be capable of operating continuously and with very little down time. For example, systems such as thermomechanical pulping (TMP) and chemimechanical pulping (CMP) systems require extremely large quantities of electrical energy to operate motors having ratings in the thousands of horsepower range for the purpose of grinding wood chips to a fine pulp at an output rate of more than 100 tons per day, for example. Extremely large quantities of waste energy are generated as a result of the conversion of the electrical power driving the motors, which electrical power is converted to mechanical work and subsequently to thermal energy in the form of steam. Steam is passed through a tube containing the wood chips prior to their entry into a primary refiner to soften the chips and thereby facilitate the refining operation.
The chips are typically defibred between a pair of huge counter-rotating discs. The heat generated during the refining operation, which is performed in a confined region, is vented to the atmosphere through an exhaust conduit. Although some efforts have been developed to recycle small portions of the vented steam to the aforementioned steaming tube in which the chips are initially heated and softened, the vast majority of the heat energy is unrecoverable and hence is lost.